51 52 53 54 55 56 57 58 59 60	61 62 63 64 65 66 67 68 69 70	71 72 73 74 75 76 77 78 79 80	81 82 83 84 85 86 87 88 89 90	91 92 93 94 95 96 97 98 99	100 101 102 103 104 105 106
	Crux	Philip E. Cryer	$The crystallographic restriction theorem in its basic form was based on the observation that the rotational symmetries of a crystal are usually limited to 2-fold, 3-fold, 4-fold, and 6-fold. However, quasicrystals can occur with other diffraction pattern symmetries, such as 5-fold; these were not discovered until 1982 by Dan Shechtman. Crystals are modeled as discrete lattices, generated by a list of independent finite translations (Coxeter 1989). Because discreteness requires that the spacings between lattice points have a lower bound, the group of rotational symmetries of the lattice at any point must be a finite group (alternatively, the point is the only system allowing for infinite rotational symmetry). The strength of the theorem is that not all finite groups are compatible with a discrete lattice; in any dimension, we will have only a finite number of compatible groups.$ Crystallographic Theorem	Crystal Palace	Crystallomancy
Cuba	Cubit	Cuckold	Cuckold’s Point	Cuckoo Spit	Cuckoo
Cudbear Orchil Lichen	Cudbear Manufactory	Culdees	Culross Girdle	Cuckoo Flower	Cuckoo Clock
	497			498